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#include <math.h>
#define POW2(x) ((x) * (x))
float
dot(float x[3], float y[3]) {
return x[0] * y[0] + x[1] * y[1] + x[2] * y[2];
}
void
normalize(float x[3]) {
float len;
int i;
len = sqrt(dot(x, x));
for(i = 0; i < 3; ++i)
x[i] /= len;
}
float
sphere_intersect(float y[3], float r[3], float s[3], float d[3], float c[3], float R) {
int i;
float D, n[3], t, v[3];
for(i = 0; i < 3; ++i)
v[i] = s[i] - c[i];
D = POW2(dot(v, d)) - (dot(v, v) - POW2(R));
if(D < 0)
return -1;
t = -dot(v, d) - D;
for(i = 0; i < 3; ++i) {
y[i] = s[i] + t * d[i];
n[i] = y[i] - c[i];
}
normalize(n);
for(i = 0; i < 3; ++i)
r[i] = d[i] - 2 * dot(n, d) * n[i];
return t;
}
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